Enhancement on configuration management

This MR clarifies the use of several buttons in the Well logs panel.

Before :

After :

The trash button was confusing. It only removed a column from the current view but no state were saved, so at reload the column was displayed again (not very useful). On the other side, QGeoloGIS had no feature to remove a column from configuration, specially when this column was broken (wrong configuration) and was not displayed.

Now we have four buttons :

The "plus" button is used to add a configured column to the well logs view. Only the configured columns that are not already displayed are proposed in list. The user can pick several items.

The "minus" button is used to remove a configured columns from the well logs view. The column to remove must be selected in the log view.

Both buttons are using a new attribute in the configuration using the display keywords (1 value to display, 0 to hide)

The "new log configuration" is used to add a measure as a log column. No change on this button

The "trash" button is now use to remove a configured column from the configuration. It use the same window as the "plus" button but with all the configuration columns in the list. The user can pick several items.

I will add some docstrings.